The present invention is directed to an electrochemical apparatus such as solid-oxide electrolyte fuel cells and fuel cell assemblies for directly converting chemical energy into electricity. More particularly, it is directed to a fuel cell assembly incorporating a thermally integrated vaporizer-reformer.
Fuel cells offer many advantages over conventional power generation systems. It is generally known that such devices are capable of delivering high quality electric power with greater efficiency and lower emissions when compared to comparably sized gas or diesel fueled generators. Further, such systems are generally modular and can fulfill a wide range of energy needs including remote site power generation, light utility, and transportation applications as well as commercial cogeneration and residential applications.
Solid oxide fuel cells are well-known devices that are capable of producing electric power at higher efficiency. However, there are a number of major hurdles including issues of operation, scale, and cost.
Known solid oxide fuel cells operate by the introduction of air into the cathode and the ionization of oxygen at the cathode/electrolyte surface. The oxygen ions move across the gas non-permeable electrolyte to the anode interface, where they react with the fuel gas flowing into the anode releasing heat and giving up their electrons to the anode. The electrons pass through the anode and separator into the next adjacent cathode.
A wide variety of fuels can be used in the electrochemical apparatus of the present invention, including hydrogen, carbon monoxide, alcohols, ammonia, methane, and gaseous- or liquid-hydrocarbon mixtures. The oxidizer gas to, be supplied to the cathode can be oxygen or an oxygen containing gas such as air.
Reformation, such as steam reformation, of carbon-containing fuels is necessary to prevent solid carbon deposition (xe2x80x9ccokingxe2x80x9d) at the high solid-oxide stack operating temperatures and also to minimize local stack temperature variations. The output fuel gas (xe2x80x9csyngasxe2x80x9d) from a reformer intended for a solid-oxide fuel cell will preferably comprise chiefly hydrogen, steam, carbon monoxide, carbon dioxide, (optional) nitrogen, and contain less than about 5 percent of methane. In most cases, the reformer must be preceded by a vaporizer to vaporize water and liquid fuel (if used) followed by a mixer to mix the steam with the fuel gas and/or vapor.
Adding the vaporizer and reformation steps to the energy conversion process adds to the cost and size of the unit. The required heat input for vaporization and reforming may be obtained from the surplus heat from the fuel cell stack operation and/or using burners or partial oxidation of the fuel stream.
Many different types of vaporizers and reformers exist in the prior art, but, known designs contain their own disadvantages. These disadvantages include bulky subassembly designs, short operating times between required cleaning, and high equipment cost. Many systems rely on partial-oxidation reforming or burners as a heat source, thereby reducing overall system fuel efficiency. Finally, many of the known reformers can produce syngas having high methane content, leading to large temperature variations in the fuel cell stack (cold spots occur when high-methane syngas contacts cells) which tend to reduce both stack power and its operating life.
Thus, electrochemical apparatus incorporating a thermally integrated vaporizer-reformer capable of high fuel to electric power efficiency is desirable. It is further desirable to create an electrochemical apparatus incorporating a thermally integrated vaporizer reformer, which is compact, low in cost, requires infrequent cleaning or maintenance, and produces a fuel gas mixture containing low methane levels.
The present invention is an electrochemical apparatus incorporating a thermally integrated vaporizer and fuel steam reformer.
It is an object of the present invention to produce an electrochemical apparatus incorporating a thermally integrated vaporizer and reformer that has a long operating life, and is of moderate size, weight, and cost.
It is another object of the present invention to provide an electrochemical apparatus with a high fuel to electric power efficiency.
It is another object of the present invention to provide an electrochemical apparatus that is compact, light weight, and can be mass produced.
The present invention provides an electrochemical apparatus including a steam reformer connected to a gaseous or vaporized fuel supply and a vaporized water supply by at least one feed tube; the steam reformer having a mixing orifice and a fuel orifice, wherein the mixing orifice is adapted to receive and mix vaporized water and fuel; a fuel cell stack positioned adjacent the steam reformer and having an air passage, and a fuel passage communicating with the fuel orifice; an annular cap positioned above the fuel cell stack and spaced apart from the stack by a sealing ring, wherein the annular cap and the sealing ring define an air inlet communicating with the air passage and adapted to channel air into the air passage; a can extending downwardly from the annular cap spaced apart from the fuel cell stack and steam reformer defining an exhaust passage therebetween; an enclosure surrounding and spaced apart from the can defining an open space therebetween which is at least partially filled with insulation; and at least one coolant inlet formed within the enclosure for receiving coolant from a source. The coolant can be the oxidizing gas.
The present invention further provides an electrochemical apparatus including an enclosure having a base, a top, and an outer wall extending therebetween; a vaporizer positioned generally centrally of the base, the vaporizer including a mixing orifice; at least one feed tube extending through the base into the vaporizer; a steam reformer positioned on top of the vaporizer and communicating with the mixing orifice, the steam reformer having a conductive output end plate defining a cell stack fuel orifice; a compact cell stack located above the steam reformer, the cell stack having at least one air passage and a fuel passage, wherein the fuel passage communicates with the fuel orifice; a stack end plate closing the cell stack, the end plate having at least one air orifice in communication with the air passage; an electrically insulated sealing ring extending upwardly from the stack end plate outside the air orifice; an annular cap mounted on top of the sealing ring and having a hot air inlet, wherein the cap extends radially outward beyond the sealing ring; a can extending downwardly from the annular cap to the base defining an exhaust passage between the cell stack and the can, which communicates with an exhaust vent (preferably annular) within the base; a porous thermal insulation surrounding and spaced apart from the can defining a hot air plenum therebetween; a pin hole sheet surrounding the can defining an open space and spaced inwardly from the enclosure to define a cold air plenum therebetween, wherein the cold air plenum receives coolant air from a coolant supply via a coolant inlet, and the pin hole sheet is provided with a pattern of perforations adapted to distribute the coolant uniformly around the circumference and along the height as desired.
The present invention further provides an electrochemical apparatus including a steam reformer having a mixing orifice, the mixing orifice being adapted to receive and mix vaporized water and fuel; a first end plate adjacent to the steam reformer, the first end plate having a fuel inlet in communication with the steam reformer, and at least one air inlet conduit in communication with an air supply; a solid oxide fuel cell stack positioned adjacent to the first end plate, and having an air passage in communication with the air conduit, and a fuel passage communicating with the fuel orifice; an electrically conductive second end plate mounted adjacent to the stack opposite the first end plate; a conducting element extending from the second end plate; a first cylindrical wall extending upwardly from the first end plate spaced from the cell stack defining an annular chamber therebetween; a second cylindrical wall extending from the first end plate opposite the first cylindrical wall and spaced apart from the steam reformer, defining an exhaust passage therebetween, at least one exhaust port formed within the first end plate, wherein the exhaust port communicates with the annular chamber and the exhaust passage, an enclosure surrounding and spaced apart from the first and second cylindrical walls defining an open space therebetween, wherein the open space is at least partially filled with insulation and wherein the enclosure defines an annular exhaust exit communicating with the exhaust passage; and a chamber extending outwardly from the enclosure defining a cold air plenum; wherein, the cold air plenum communicates with the open space and a coolant supply. The coolant can be the oxidizing gas.
The present invention further provides and electrochemical apparatus including a steam reformer having a mixing orifice and a fuel orifice, the mixing orifice being adapted to receive and mix vaporized water and fuel; a first end plate adjacent to the steam reformer, the first end plate having a fuel inlet communicating with the fuel orifice and at least one exhaust conduit; a cylindrical wall extending from the first end plate surrounding the steam reformer and spaced therefrom defining an exhaust passage therebetween, wherein the exhaust passage is in communication with the exhaust conduit; a solid oxide fuel cell stack sandwiched between the first end plate and a second end plate; said solid oxide fuel cell stack defining at least one exhaust passage in communication with the exhaust conduit and a fuel passage communicating with the fuel orifice; porous insulation surrounding the solid oxide fuel cell stack and spaced therefrom defining a hot air plenum therebetween; an enclosure surrounding said porous insulation wherein said enclosure defines an exhaust exit registerable with the exhaust passage, and wherein the enclosure is in communication with an oxidant gas supply.